1. Technical Field of the Invention
The present invention relates generally to stators for electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators.
More particularly, the invention relates to a stator for an electric rotating machine which includes restraints for restraining relative radial movement between turn portions of electric wires; the electric wires make up a stator coil of the stator, with the turn portions located outside of slots of a stator core of the stator to form coil ends of the stator coil.
2. Description of the Related Art
In recent years, electric rotating machines, such as electric motors and electric generators, have been required to be compact, be able to output high power, and have high quality.
In particular, for electric rotating machines for use in motor vehicles, the spaces available for installation of those machines in the motor vehicles have been decreasing, while the need for them to output high power has been increasing. Moreover, it has also been required to improve the reliability of those electric rotating machines.
Japanese Unexamined Patent Application Publication No. 2000-166158 discloses a winding method for reducing stresses on insulating paper sheets interposed between a stator coil and a stator core of a stator for an electric rotating machine. More specifically, according to the winding method, spacers are first mounted on the axial end faces of the stator core which has the insulating paper sheets arranged in slots thereof. Then, the stator coil is wound around the stator core so that the insulating paper sheets are interposed between the stator core and the stator coil and the spacers are interposed between the axial end faces of the stator core and the stator coil. Thereafter, the spacers are removed from the stator core and the stator coil which together constitute the stator for the electric rotating machine. Consequently, with the use of the spacers, it is possible to reduce stresses which are imposed on the insulating paper sheets during the winding of the stator coil, thereby ensuring the insulation properties of the insulating paper sheets and improving the reliability of the electric rotating machine.
Japanese Unexamined Patent Application Publication No. 2006-33918 discloses a stator for an electric rotating machine which includes field-relaxing blocks. More specifically, the field-relaxing blocks are made of a metal or resin and have a circular or triangular cross-section. The field-relaxing-blocks are mounted on the axial end faces of teeth of a stator core of the stator, thereby preventing electric field from concentrating on the axial end of the stator core.
However, neither the spacers disclosed in Japanese Unexamined Patent Application Publication No. 2000-166158 nor the field-relaxing blocks disclosed in Japanese Unexamined Patent Application Publication No. 2006-33918 can restrain relative radial movement between turn portions of electric wires that make up the stator coil. More specifically, each of the electric wires has a plurality of in-slot portions, each of which is received in a corresponding one of the slots of the stator core, and a plurality of turn portions each of which is located outside of the slots of the stator core to connect one adjacent pair of the in-slot portions of the electric wire.
Without restraining relative radial movement between the turn portions of the electric wires, during operation of the electric rotating machine, the turn portions may spread radially (i.e., in the radial direction of the stator core) due to vibration and/or thermal and mechanical stresses imposed thereon, causing the in-slot portions of the electric wires to radially spread as well. Consequently, the stator coil may protrude radially inward from the stator core to make contact with a rotor which is disposed radially inside of the stator core to constitute, together with the stator, the electric rotating machine. As a result, either or both of the stator coil and the rotor would be damaged, thereby lowering the reliability of the electric rotating machine.